Korean powder keg

North Korea's recent threats to target South Korean and American cities with atomic destruction have the shrill belligerence of a 6-year-old's temper tantrum. But while few analysts believe North Korea has the means to carry out its threats, U.S. and South Korean officials would nevertheless be unwise to ignore them. With tensions on the peninsula higher than at any time since the end of the Korean War, there's great danger a conflict could break out by accident or through miscalculation.

So far, the Obama administration has taken a measured response to North Korea's provocations, which is the only reasonable course in this situation. Defense Secretary Chuck Hagel announced last week that the U.S. will beef up its missile defense systems in the Pacific and on the American west coast, and he delayed a planned test this month of a long-range U.S. nuclear missile in order to ease tensions — all prudent steps designed to demonstrate America's resolve not to be intimidated by North Korea's bluster without inflaming the situation.

That's because the key to moving forward lies less in attempting to appease the threatening rhetoric of Kim Jong Un, the 28-year-old North Korean leader who inherited the country's top post from his father last year, than in developing a more productive relationship with new China's new president, Xi Jinpeng, whose government remains the North's biggest backer.

The last thing China wants to see is a military conflict erupt on the peninsula that could lead to the collapse of Mr. Kim's regime and precipitate a flood or refugees across its border with North Korea. Nor does China wish to contemplate the prospect of a regional arms race in which South Korea, Japan, Taiwan, Vietnam and possibly others all feel they have to develop their own nuclear arsenals in order to deter North Korea. In recent weeks China's President Xi has voiced increasing impatience with North Korea's irresponsible saber-rattling, but Mr. Kim so far has chosen to ignore the warning.

Tensions have been rising on the Korean peninsula ever since the United Nations slapped new sanctions on North Korea following its third underground nuclear test in February. That test, which suggested North Korea had the capacity to build a Hiroshima-size weapon, followed the country's launch of a long-range ballistic missile last year. It's still unclear whether North Korea has developed a nuclear warhead small enough to fit atop one of its missiles.

What there's no doubt about is that the country's aggressive posturing fits a pattern of previous provocations aimed at extracting concessions from its neighbors and the international community. Mr. Kim clearly wishes to emulate his father's success in extorting "protection money" — in the form of fuel and food aid and an easing of economic sanctions — as his price for ratcheting down tensions. Once the elder Mr. Kim got what he wanted, he invariably broke his promises to disarm.

We've bought that horse too many times before for the Obama administration to fall for the same trick again. By now it should be clear to everyone that rewarding North Korea's bad behavior will only encourage more of the same in the future.

Instead, the U.S. needs to work with China — and to a lesser extent Russia, which has expressed similar concerns — to put pressure on North Korea to comply with international norms of behavior. If anyone has influence over how North Korea calculates the risks and benefits of its actions it is China, which could make life very uncomfortable for its reclusive neighbor if it chose to halt shipments of food and fuel across the border.

China has a huge interest in maintaining North Korea as a communist buffer state between it and capitalist South Korea, where 28,000 U.S. troops are stationed. That's why it doesn't want North Korea to collapse into chaos and possibly be absorbed into a reunified Korean nation governed from Seoul. At the same time, China's president can't ignore the possibility that Mr. Kim's reckless provocations are in fact destabilizing the entire region in a way that makes that outcome more rather than less likely.

The Obama administration can hardly expect China to step up the pressure on Mr. Kim merely because it would be in our interest for it to do so. But if it can persuade Mr. Xi that China ultimately has as much to lose as we do from Mr. Kim's nuclear bluster, it could open the way for a new strategic cooperation between the U.S. and China in ensuring regional stability that works to the advantage of both countries.